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oral Presentation 3-06 Combined Effect of SO2 Uptake and Steam Explosion on Ethanol Production from Lignocellulosics
I. De Bari, E. Viola, D.
Barisano, M. Cardinale, F. Nanna, and F. Zimbardi ENEA – Renewable Energy Division
Policoro (MT) 75025,
Italy
Telephone: (39) 835-974486;
Fax: (39) 835-974210; E-mail:
zimbardi@trisaia.enea.it The ethanol production from
lignocellulosic biomass can be achieved by several methods. Steam Explosion (SE) is one of the most
efficient, as it provides a substrate suitable for enzymatic hydrolysis. In many cases the hydrolysis of the chemical
bonds caused by the saturated steam and acetic acid from organic decomposition
ensures a fiberization that positively affects the subsequent bioconversion
steps. Some lignocellulosics are
particularly resistant to the SE treatment, and the high severity required to
overcome this drawback reduces the sugar recovery; alternatively, chemicals are
added to catalyse the hydrolysis reactions. In this work the effect of
softwood impregnation by SO2 has been investigated, both in terms of
chemical modification and effect on the enzymatic hydrolysis and fermentation,
with the aim of optimising the cellulose bioconversion in ethanol. Aspen wood has been humidified at 35% and
exposed overnight to SO2 in a hermetic tank, and then steam exploded
in a 10-liter batch reactor at 205°C for 3 or 10 minutes. The gas uptake has been determined by
weighting and resulted 18 g/kgwood; it has been pointed out that
all the gas desorbs if dry wood is used.
The treated wood has been extracted with warm water; the extract and the
solid residue have been analysed and their composition has been compared with
that of SE wood, without SO2 pre-adsorption. The SO2 pre-adsorption results in
a higher sugar solubility, particularly glucose, with an increased ratio of
monomeric to oligomeric forms. In both procedures, the
sugar solubility increases at high severity while cellulose DP decreases; under
the investigated condition, the cellulose DP is halved by the SO2
action. The solid residues were used to
carry out Simultaneous Saccharification and Fermentation by using commercial
enzymes and the yeast Saccharomices cerevisiae. In the case of wood not exposed, the
hydrolysis yield increases with the SE severity while the treatment severity
does not affect the hydrolysis yield in the case of pre-impregnated wood. In the latter case it has been the maximum
cellulose hydrolysis yield of 85%. The
ethanol yield reaches the maximum value of 82% when the wood is impregnated
with SO2. While in the case
of wood not exposed the ethanol yield increases with the SE severity, a
slightly lower ethanol production is obtained from the wood impregnated with SO2
and treated at the higher SE severity.
This result could be related to the residual inhibitors. As a whole, the SO2
pre-adsorption plays the same role of increasing severity, but without the side
effect of sugar degradation.
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